I have data of the form tC <- textConnection(" Subject Date parameter1 bob 3/2/99 10 bob 4/2/99 10 bob 5/5/99 10 bob 6/27/99 NA bob 8/35/01 10 bob 3/2/02 10 steve 1/2/99 4 steve 2/2/00 7 steve 3/2/01 10 steve 4/2/02 NA steve 5/2/03 16 kevin 6/5/04 24 ") data <- read.table(header=TRUE, tC) close.connection(tC) rm(tC)
I am trying to calculate rate of change of parameter1 in units/day for each person. I think I need something like: "lapply(split(mydata, mydata$ppt), function(x) lm(parameter1 ~ day, data=x))" I am not sure how to handle the dates in order to have the first day for each person be time = 0, and the remaining dates to be handled as days since time 0. Also, is there a way to add the resulting slopes to the data set as a new column? Thanks, Marcel -- View this message in context: http://r.789695.n4.nabble.com/regression-on-data-subsets-in-datafile-tp3806743p3806743.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.